MPEGLAYER3WAVEFORMAT Structure

MPEGLAYER3WAVEFORMAT Structure   Microsoft DirectShow 9.0 MPEGLAYER3WAVEFORMAT Structure The MPEGLAYER3WAVEFORMAT structure describes an MPEG Audio Layer-3 (MP3) audio format. Syntaxtypedef struct mpeglayer3waveformat_tag { WAVEFORMATEX wfx; WORD wID; DWORD fdwFlags; WORD nBlockSize; WORD nFramesPerBlock; WORD nCodecDelay; } MPEGLAYER3WAVEFORMAT; Members wfx WAVEFORMATEX structure that specifies the basic audio format. The wFormatTag member must be WAVE_FORMAT_MPEGLAYER3. The cbSize member must be at least 12. (For cbSize, you can use the constant MPEGLAYER3_WFX_EXTRA_BYTES, defined in the Mmreg.h.) wID Set this structure member to MPEGLAYER3_ID_MPEG. fdwFlags Indicates whether padding is used to adjust the average bitrate to the sampling rate. Use one of the following values: Value Description MPEGLAYER3_FLAG_PADDING_ISO Insert padding as needed to achieve the stated average bitrate. MPEGLAYER3_FLAG_PADDING_ON Always insert padding. The average bit rate may be higher than stated. MPEGLAYER3_FLAG_PADDING_OFF Never insert padding. The average bit rate may be lower than stated. nBlockSize Block size in bytes. This value equals the frame length in bytes x nFramesPerBlock. For MP3 audio, the frame length is calculated as follows: 144 x (bitrate / sample rate) + padding. nFramesPerBlock Number of audio frames per block. nCodecDelay Encoder delay in samples. If you do not know this value, set this structure member to zero. Remarks If you are using an audio compression manager (ACM) codec, you can use the acmFormatEnum function to fill in this structure.

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